Radiocommunication networks were originally developed primarily to provide voice services over circuit-switched networks. The introduction of packet-switched bearers in, for example, the so-called 2.5G and 3G networks enabled network operators to provide data services as well as voice services. Eventually, network architectures will likely evolve toward all Internet Protocol (IP) networks which provide both voice and data services. However, network operators have a substantial investment in existing infrastructures and would, therefore, typically prefer to migrate gradually to all IP network architectures in order to allow them to extract sufficient value from their investment in existing infrastructures. Also to provide the capabilities needed to support next generation radio communication applications, while at the same time using legacy infrastructure, network operators could deploy hybrid networks wherein a next generation radio communication system is overlaid onto an existing circuit-switched or packet-switched network as a first step in the transition to an all IP-based network. Alternatively, a radio communication system can evolve from one generation to the next while still providing backward compatibility for legacy equipment.
One example of such an evolved network is based upon the Universal Mobile Telephone System (UMTS) which is an existing third generation (3G) radio communication system that is evolving into High Speed Packet Access (HSPA) technology. Yet another alternative is the introduction of a new air interface technology within the UMTS framework, e.g., the so-called Long Term Evolution (LTE) technology. Target performance goals for LTE systems include, for example, support for 200 active calls per 5 MHz cell and sub 5 ms latency for small IP packets. Each new generation, or partial generation, of mobile communication systems add complexity and abilities to mobile communication systems and this can be expected to continue with either enhancements to proposed systems or completely new systems in the future.
Local Call Local Switch (LCLS) is an ongoing work item within the 3GPP standardization groups GERAN (GSM/EDGE Radio Access Network) and CT (Core Network and Terminals) which is intended to save transmission resources of the Abis and/or A-interface. The LCLS feature provides the capability for the user plane (i.e. the voice data path) to be locally switched within the BSS (e.g. voice data in user plane is not backhauled to the CS Core Network) for calls that are generated and terminated by users that are served by the same BSS. The result is saving of transmission resources on the Abis and/or A-interface. LCLS may be supported on both TDM based A-interface (AoTDM) and IP based A-interface (AoIP). The stage 2 work of the LCLS feature is specified in the 3GPP Technical Specification 23.284 bounded for Release-10 in March 2011.
However, there remain a number of issues regarding how to, for example, handover a user equipment (UE) that has an ongoing call which is locally switched to a target BSS or RNS which does not support the LCLS feature.